Influenza Surveillance

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Influenza Surveillance

• Raymond A. Strikas, M.D.
• National Vaccine Program Office
• Department of Health and Human Services
• With thanks to Lynnette Brammer
• Influenza Branch
• Centers for Disease Control and Prevention

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Interpandemic Influenza

• Illness in 5-20 population each year
• Highest attack rates in children
• Highest rates of hospitalization and death in the
  elderly

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Objectives of Influenza Surveillance

• Determine which influenza viruses are
  circulating where are they circulating when are
  they circulating
• Determine intensity and impact of influenza
  activity
• Detect unusual events
• Infection by unusual viruses
• Unusual syndromes caused by influenza viruses
• Unusually large/severe outbreaks of influenza

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Practical Uses of Influenza Surveillance Data

• Vaccine strain selection
• Treatment decisions
• Public health resource allocation
• Influenza prevention and control policy
• Pandemic planning
• General Information public and media

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Influenza Surveillance What Are We Trying to
Measure?
U.S. population 300 million
Lab Tested
Hospitalizedgt200,000
10-20 Infected (30-60 million)
Seek Care
Death 36,000
50 Symptomatic (15-30 million)
Treat at Home
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Influenza Surveillance Challenges

• Counting individual cases is impractical
• Not everyone with influenza accesses healthcare
• Cant distinguish influenza from other
  respiratory viruses on clinical criteria
• Most cases are not tested / lab confirmed
• Timing of specimen collection is challenging
• Rapid antigen testing sensitivity gt 70,
  variation across tests
• Culture within 3 days of onset
• Serology acute within 1 wk of onset,
  convalescent 2-3 wks later
• Volume cant test all respiratory cases
• Reporting (virus isolation/illness) is not
  mandatory

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Influenza Surveillance Challenges

• Many cases with severe influenza-related
  complications (hospitalization or death) wont
  test positive
• Few primary viral pneumonias
• Most due to secondary infections and worsening of
  chronic conditions
• Data must be timely!
• Influenza activity that occurs this week will be
  reported next week

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U.S. Influenza Surveillance

• Virologic surveillance
• Preliminary data reported
• Proportion of influenza virus type/subtypes
• Antigenic characterization - vaccine match
• Indirect measures or tracking systems are used
  to monitor impact
• Influenza-Like Illness (ILI)
• Pneumonia and Influenza morbidity/mortality
  (PI)
• Estimates of overall influenza activity by state
• Determine periods of excess ILI or death
• Surveillance for pediatric hospitalization and
  death
• Population-based rates calculated

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U.S. Influenza Surveillance
State and Territorial Epidemiologists
Pediatric Hospitalization
Pediatric Mortality
Health Departments
Vital Statistics Registrars
Sentinel Providers
CDC
Laboratories
Other
Public Health Officials
Public
Physicians
Media
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Virologic Surveillance in the U.S.

• 125 participating laboratories
• Weekly reports
• specimens tested
• positive for influenza type, subtype, age
• Specimens collected during routine patient care

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WHO/NREVSS Collaborating LaboratoriesNational
Summary, 2005-06
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• Morbidity and Mortality Surveillance

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Sentinel Provider Network Overview

• Purpose monitor outpatient visits for ILI
• Collaborative effort between CDC and state health
  departments
• gt2,000 physicians/clinics enrolled for the
  2005-06 season
• Weekly reports
• Total of patient visits
• visits for influenza-like illness (ILI) by age
  group
• ILI fever ? 100 F (38 C) and cough or sore
  throat, in absence of a known cause
• Can submit specimens for culture
• Early, peak, and late season

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Percentage of Visits for Influenza-like
IllnessReported by Sentinel Providers 2003-2004
through 2005-06 Seasons
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State Epidemiologists Report

• Assesses overall influenza activity at state
  level
• None, sporadic, local, regional, widespread
• Incorporates virus circulation illness
• Only system reporting state-level data
• Allows local interpretation of surveillance data

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Influenza Activity Levels

• No Activity No laboratory-confirmed cases of
  influenza and no reported increase in the number
  of cases of ILI
• Sporadic Small numbers of laboratory-confirmed
  influenza cases or a single influenza outbreak
  has been reported, but there is no increase in
  cases of ILI
• Local Outbreaks of influenza or increases in ILI
  cases and recent laboratory-confirmed influenza
  in a single region of the state
• Regional Outbreaks of influenza or increases in
  ILI and recent laboratory confirmed influenza in
  at least 2 but less than half the regions of the
  state
• Widespread Outbreaks of influenza or increases
  in ILI cases and recent laboratory-confirmed
  influenza in at least half the regions of the
  state

. . . . .
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Weekly Influenza Activity Estimates Reported by
State Territorial Epidemiologists Week ending
May 6, 2006 - Week 18




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122 Cities PI Mortality Reporting System

• Purpose monitor PI related mortality in a
  timely manner
• Weekly reports from vital statistics offices in
  122 US cities
• Total of death certificates filed
• with pneumonia or influenza listed anywhere
• 1/4 to 1/3 of US deaths
• Timely
• Certificates received within 8 days of death
  reported to CDC within another 7 days

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Pneumonia and Influenza Mortality for 122 U.S.
CitiesWeek Ending 5/6/2006
Epidemic Threshold
Seasonal Baseline
2001
2002
2003
2004
2005
10 20 30 40 50 10
20 30 40 50 10 20
30 40 50 10 20
30 40 50 10
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National Center for Health Statistics Mortality
Data

• Provides a complete and more detailed record of
  cause of death
• gt 99 of all deaths in the US
• Separate record for each individual
• Basic demographic data
• Date of death
• Underlying contributing causes of deaths
• Data used for special studies
• Mortality estimates obtained from mathematical
  modeling
• Not available until 2 yrs later

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Influenza-Associated Pediatric Mortality Case
Definition

• Requested data on pediatric deaths during the
  2003-04 season
• 153 deaths in 40 States
• June, 2005, Council of State and Territorial
  Epidemiologists (CSTE) adopted proposal to make
  influenza-associated death in a person lt18 yrs. a
  nationally notifiable condition
• Data reported weekly in MMWR and influenza update
• Death resulting from a clinically compatible
  illness that was confirmed to be influenza by an
  appropriate laboratory or rapid diagnostic test
• In a person aged lt18 years
• With no period of complete recovery between the
  illness and death

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Pediatric Hospitalization Surveillance

• Pediatric hospitalization
• Emerging Infections Program (EIP) 11 sites
• children lt18 yrs hospitalized with
  laboratory-confirmed influenza infection
• New Vaccine Surveillance Network (NVSN) 3 sites
• children lt5 yrs hospitalized with
  laboratory-confirmed influenza infection

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EIP Influenza Laboratory-Confirmed Cumulative
Hospitalization Rates for Children 0 - 4 Years
and 5-17 Years, 2003-04 through 2005-06
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U.S. Influenza Surveillance
State and Territorial Epidemiologists
Pediatric Hospitalization
Pediatric Mortality
Health Departments
Vital Statistics Registrars
Sentinel Providers
CDC
Laboratories
Other
Public Health Officials
Public
Physicians
Media
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U.S. Contribution to International Influenza
Surveillance

• Participates in WHO Global Influenza Program
• 112 National Influenza Centers (NIC) in 83
  countries
• 4 international reference centers
• Atlanta, London, Melbourne, Tokyo
• CDC is a reference center but also acts as a NIC
  for the U.S.
• Report weekly data from U.S. WHO and NREVSS
  collaborating labs to WHO via FluNet
• Use Sentinel Physician data in combination with
  virologic data to characterize influenza activity
  in the U.S. weekly
• Weekly submission of U.S. summary
• Contributes data for vaccine strain selection

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Vaccine Safety and Effectiveness Monitoring

• Safety (http//www.cdc.gov/nip/menus/vacc_safety.h
  tm)
• Vaccine Adverse Events Reporting System (VAERS)
• Vaccine Safety Data Link (VSD)
• Clinician Immunization Safety Assessment (CISA)
• Effectiveness
• Selected EIP sites for children
• Ad hoc studies